Tantalum base alloys



United States Patent 3,140,943 TANTALUM BASE ALLOYS Alexander L. Field, Jr., Pittsburgh, Robert L. Amman, Pleasant Hills, and Allen I. Lewis, deceased, late of Forest Hills, Pa., by Bernard J. Ambrose, administrator, Monroeville, Pa., assignors to Westinghouse Electric (Iorporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Jan. 17, 1962, Ser. No. 167,473

3 Claims. (Cl. 75-174) The present invention relates to tantalum base alloys suitable for use where high strength and ductility at either sub-zero or elevated temperatures is required.

Fabricable alloys possessing strength and ductility at extremely high and extremely low temperatures have many industrial and military applications, and it is generally recognized that future developments in many fields are closely tied to the availability of new and improved alloys possessing these properties. For example, the development of improved rocket nozzles and blades for gas turbines is dependent upon the availability of such alloys.

In accordance with this invention, it has been found that workable alloys possessing unusually high strength and ductility at temperatures above 2000 F. and at temperatures as low as 320 F. can be produced by alloying tantalum, columbium and hafnium in specified proportions.

The object of the invention is to provide a readily workable cast member comprising predetermined proportions of hafnium and columbium, the balance, over 50% by Weight being tantalum, with small amounts of incidental impurities, the cast member being characterized by relatively high strength at elevated temperatures and by relatively good ductility at room and sub-zero temperatures.

Other objects of the invention will, in part be obvious and will, in part, appear hereinafter.

In accordance with the present invention wrought members have been produced from a cast member comprising a ternary tantalum base alloy comprising from 1 to 8% by weight of hafnium, from 1 to 8% by weight columbium and the balance being tantalum, with small amounts of incidental impurities. The alloys are characterized by high mechanical strength and ductility at elevated and sub-zero temperatures, and the ability to be easily wrought to shape by hot or Warm Working, or in certain alloy compositions by cold working. In a preferred embodiment, the alloys of this invention comprise from 2 to 6% by weight hafnium, from 2 to 6% by weight columbium and the balance being tantalum, with small amounts of incidental impurities. Incidental impurities and small amounts of additives may include zirconium, tungsten, cobalt, nickel, and iron in amounts of less than 1% The alloy may be melted by one of several procedures which will ensure homogeneity and a minimum of contamination. For example, unalloyed high-purity tantalum together with the proper amounts of hafnium and columbium can be fed into a conventional nonconsumable arc melting furnace containing an inert atmos phere such as argon, or a vacuum. The resulting ingot should be remelted several times, preferably by consumably arc melting it, to achieve homogeneity, then it may be hot worked to the desired shape. The alloy may also be prepared by pressing together powders of tantalum, hafnium and columbium and consumably arc melting the same. Levitation melting of a ball or rod of the alloy, using induction heating, or electron beam melting is also satisfactory.

The following example is illustrative of the present invention.

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An alloy of the following composition was prepared by consumable are melting: 92% tantalum, 4% hafnium and 4% columbium. The consumable electrode was prepared by blending 20 mesh powders of tantalum, hafnium and columbium by suitable mechanical miX- ing, compacting the same into bars at 50 tons per square inch pressure and sintering in a vacuum at 3000" F. for two hours. The bars were then are melted in a conventional furnace having a vacuum of less than 1 micron pressure using a 60 cycle single phase AC. power at 2800 amperes and 20 volts for a inch by inch cross-section electrode. The melting rate was about 1 /2 pounds per minute. The resulting billet, coated With a glass for lubrication and oxidation protection, was then extruded at a temperature of 3 100 F. at a pressure of 1800 psi. The extruded bar was then rolled at 220 F. with 50 mils reduction per pass. The sheet or strip was then stress-relieved for one hour at 2015 F. Samples were cut from the resulting sheet and were tested at temperatures ranging from -320 F. to 2700 F. for ultimate tensile strength, yield strength, percent elongation and percent reduction in area. The following results were obtained:

Ultimate 0.2% Yield Percent Test; Temp. F.) Tensile Strength Percent Reduction Strength (p.s.i.) Elongation in Area It will be evident from these tests that the alloy has a relatively high strength and ductility at both sub-zero and at elevated temperaures.

Other alloys containing from 1% to 8% columbium and from 1% to 8% of hafnium, balance tantalum may be prepared with good properties.

It will be understood that the above description is only exemplary and not in limitation of the invention.

We claim as our invention:

1. A readily workable cast member comprising a tantalum base alloy consisting essentially of by weight from 1 to 8% hafnium, from 1 to 8% columbium and the balance tantalum, except for incidental impurities, the cast member being characterized by relatively high strength at elevated temperatures and by relatively good ductility at room and sub-zero temperatures.

2. A readily workable cast member comprising a tantalum base alloy consisting essentially of by weight from 2 to 6% hafnium, from 2 to 6% columbium and the balance tantalum with small amounts of incidental impurities, the cast member being characterized by relatively high strength at elevated temperatures and by relatively good ductility at room and sub-zero temperatures.

3. A readily workable cast member comprising a tantalum base alloy consisting essentially of by weight 4% hafnium, 4% columbium and the balance tantalum with small amounts of incidental impurities, the cast member being characterized by relatively high strength at elevated temperatures and by relatively good ductility at room and sub-zero temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 1,881,315 Honda et a1. Oct. 4, 1932 FOREIGN PATENTS 201,297 Austria Dec. 27, 1958 1,244,055 France Sept. 12, 1960 

1. A READILY WORKABLE CAST MEMBER COMPRISING A TANTALUM BASE ALLOY CONSISTING ESSENTIALLY OF BY WEIGHT FROM 1 TO 8% HAFNIUM, FROM 1 TO 8% COLUMBIUM AND THE BALANCE TANTALUM, EXCEPT FOR INCIDENTAL IMPURITIES, THE CAST MEMBER BEING CHARACTERIZED BY RELATIVELY HIGH STRENGTH AT ELEVATED TEMPERATURES AND BY RELATIVELY GOOD DUCTILITY AT ROOM AND SUB-ZERO TEMPERATURES. 